1. Field of the Invention
This invention concerns an oriented polyolefin film having excellent blocking-resistance, favorable transparency and high strength. More specifically, this invention relates to an oriented polyolefin film which contains particles of a condensated resin with an average particle size of 0.5 to 10 .mu.m comprising a compound having a triazine ring as a structural unit in an amount of 0.01 to 0.1% by weight based on the polyolefin and which is oriented monoaxially or biaxially by a factor of at least 4 in the orienting directions.
2. Description of the Prior Art
Polyolefin films, particularly oriented polyolefin films, are mainly used as packaging materials for food stuffs or other like substances. However, the oriented poloyolefin films have a major drawback in that they tend to cause blocking and thereby significantly reduce manageability for packaging and other like operations.
In view of the above, means for preventing the blocking in the films that have hitherto been employed have included such techniques as blending fine inorganic silica or talc powder, etc., with the polyolefin to formulate a polyolefin composition, which is then molded during melting to obtain polyolefin film. However, a great amount of inorganic powder has to be mixed in order to provide a polyolefin composition with a satisfactorily high blocking resistance. On the other hand, the polyolefin composition in admixture with a great amount of fine inorganic powder has the defect that it lacks strength when formed into oriented films. Further, voids are formed at the periphery of the inorganic powder when the polyolefin films are oriented. These voids reduce the transparency of the oriented films and, thereby, noticeably impair the commercial value of the films as a packaging material.
In order to overcome the foregoing drawbacks, a method of blending fine polyamide powder instead of the fine inorganic powder has been proposed. Blending of the fine polyamide powder can indeed prevent the reduction in the transparency of the resulting polyolefin films. However, it is again necessary to blend a great amount of fine polyamide powder in order to provide the resultant polyolefin films with a sufficient blocking resistance, which leads to unsatifactory physical properties such as reduction in the strength of the polyolefin films. Moreover, since this increases the film cost and causes an economical disadvantage, no general industrial application thereof has yet been achieved.